Sound reproducer



WVHIIIMORE June 5, lszsk v SOUND REPRODUCERQ Filed Aug. 15, 1927 2 Sheets Sheat l Patented June 5, 1928.

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WILLIAM B. WHITMOBE, ORANGE, NEW JERSEY.

SOUND BEPRODUCER.

Application filed August 15, 1927. Serial No. 212,944.

This invention relates to a sound reproducer and amplifier, famiharly known as a loud speaker and more particularly relates tothe vibratory element, commonly calledity, the shading, inflection, tempo. and pecul-.

- iar background characteristic, in exact reproduction of the original efi'ort, without omission-or i; .tiition, except as to volume.

' Accordingly, 'the principal object of the invention is to provide a loud speaker having the above charactertistics, and a further object of the invention isto provide a loud speaker of the character described whlch may. serve toamplify the reproduction without lessening the quality thereof.

' Another object of the invention is to provide a vibratory element or diaphragm, which is adapted foruse with standard telephonic units to obtain the reproduction and amplification of sounds having the characteristics above mentioned.

Another object of the invention is,to provide a loud spreaker of thecharacter described, and one which is simple and inexpensive in construction.

Other objects of the invention will be in part obvious and in part pointed out herein after.

It has been discovered that when a membrane is maintained under tension along lines which converge toward orat a point or apex on the membrane, the quality of the sound reproduction is greatly improved over the quality of sound reproduction that can be obtained from membrances tensioned along divergent lines, as for instance, membranes which are stretched fiat across a frame. or membranceswhich are sufficiently rigid to beself-maintaining in their operat tached to the membrane, preferably at the point of convergence of the lines of tension or at the point or points of application of force causing the tension.

It is an accepted principle in.the science of sound that a good conductor of sound waves has a low density as compared to its stiffness. It appears, therefore, that in practically all instances, a good sound conductor is' a good sound reproducer, and, therefore, the above cited principle appears to apply to sound reproducers. If -now a material of low density and of practically no stiffness is placed under tension to thereby increase its stiffness, without increasing its density, it is found that its sound reproducing properties are improved. It has been known that this advantage has been obtained to some degree when a small area, say about four to five square inches, of material of low density and of low stiffness, is tightly stretched in a flat plane. However, this advantage decreases as the area increases'other things being equal, and, therefore, there has heretofore been substantially no success in producing loud speakers employing a large area of material of low density and of low stiffness and increasing the stiffness by stretching in a flat plane.

It has been discovered that a relatively large area of material of low density and low stiffness may be placed under tension by forcing some portion of the same out of the flat plane in which it would normally fall if not forced. The forcing of the material out of.its flat plane causes the material to, be

curved toward the point or points of application of force. It has been found by use and experiments that such a curved surface under tension. produces a very satisfactory sound reproduction when vibrated. In fact the production thus obtained appears to truly represent the original production without having the extraneous noises usually noted in loud speakers heretofore produced.

In defining the contour or curvature which a membrane may take in the construction herein shown, it may be stated that all parts thereof, or substantially all parts of the vibrating surface of the membrane will fall within a surface generated by a straight line having one end at the apex and passing through and following the contour of the periphery of the membrane.

There are numerous ways of building a I In loud speaker in accordance with, and wlth- I out departing from the scope of this invention.

invention will be described hereinafter for Several possible modifications of the the purposes of illustration, reference being bad to the accompanying drawings, forming a art of this. application, and in which:

ig. 1 is a front view of a loud speaker embodying'the invention in one form;

Fig. 2 is a rear view thereof;

Fig. 3 is a sectional view thereof and is taken on the lines 22 of Figs. land 2.

Fig. 4 is an enlarged fragmentary detail taken at the apex of the two tensioned membranes;

Fig. '5 is a front view of a loud speaker illustrating another form in which my invention-may be -embodied;

Fig. 6 is a sectional view thereof, and is taken on the lines 6 6 of Fig. Fig. 7 is a fragmentary detail taken at the apex showing an adjustable form of attachment; and g Figs. 8, 9, 10, 11 and 12 are respectively sectional views of several other diiferent forms of loud speakers which embody the.-

invention.

Similar reference characters refer to similar parts throughout the several views of the drawings.

Referrin to the drawings the speaker illustrated in Figs. 1, 2, 3 and 4 preferably comprises a frame of suitable .ma-terialhaving rigidity. A membrane 21 is secured to one si e of this frame by any suitable means, for instance by. nails or tacks 22, or

' with or without a suitableadhesive or other attachment means. Qn the; other side of frame 20, members 23 form arectangle to which another membrane 24 is secured by any suitable means, for instance'by' nails or tacks 25, or otherwise. In this preferred form these two membranes are drawn and secured together at the desired points so as connected with the rod 26 so that the vibrations of the telephonic unit will be applied to both of the membranes simultaneously at the. oint where they are clamped"to ether. If desired the telephonic unit may die attached at any desired, point so long as the I ness.

cated.

Preferably .the membranes 21 and 24 are I under tension which keeps them taut, and preferably are also treated with a suitable shrinking compound which may further increase thetension and which gives a more uniform distribution or balancing of strain. Whether it is advisable to apply the shrinking compound depends somewhat on the ma terials of which the membranes are made. For'instance, if fabric is used for the membrane, it is advantageous to apply a sufficient amount of shrinking compound, one form of which is commonly known as aero-' plane dope, to accomplish thedesired stiff- If desired 'any other suitable compound may be, used for this purpose. In the form illustrated in Figs. 1 to 4 inclusive, ity is preferred to first attach the smaller membrane to the frame, then join the two membranes together, then aflix the second membrane to the frames and then apply the. shrinking compound to both membranes.

It will be seen that the desired tensioning of the membranes may be accomplished in one or more of the followin ways: tensioning the membranes by stretching when aflixing the same to frame 20, by drawing the membranes to each other to a greater-or less extent, and by varying the amount and lo-. cation of the shrinkin material or compound. lnithgiapplicat on of the latter, it is to, be under jthat the whole membrane may-{be conered--elua1ly' with the sh'rinki'n and atj'a portion of the mem rane may haveione or more additional applications thereby varying the tension in t Preferably the membrane is so shaped and tensioned that the lines of tension converge centrally on the membrane at a pronounced apex thereof, although the membrane may be so shaped that it ma be put under sulficienttension without t e membrane being distorted to any materialextent out of a flat plane.

As illustrated in Figs. 5, 6 and 7 there is shown one means whereby the membrane, such as 33, is maintained under tension and maybe adjusted so that, the tension may be varied after assembly. Figs. 5, 6 and 7 also illustrate that it is not necessary to provide two membranes, each serving to tension the other, but that the tension means ma oomrise a resilient member such as 34 w ich is in no sense a membrane, in that it has no sound emitting characteristics. Membrane 33 is secured to one side of-frame 35' and resilient tensionin the other side of rame 35. A-rod 36 penetrates membrane 33, whichis secured to this red. between two nuts 37. The end of rod 36 emembrane as a whole and in partQ member 34 is secured to lUU projects through thestrip 34 of resilient marod whereby the membrane 33 may be drawn more tightly toward strip 34 or may be allowed to recede therefrom to vary the ten- 7 means of a bolt 41, or may be spaced apart as shown in Fig. 8. As shown in this figure, membranes 42 and 43 are secured to opposite sides of frame 44. Membrane 42 is clamped to bolt 41 between two nuts 45. Nut 46 engages membrane 43 so that by adjusting the nut 46 the two membranes may be drawn closer together to increase the tensioning or may be allowed to recede from each other to lessen the tensioning. The vibrations set up in the telephonic unit 47 aretransmitted to the bolt 41 to set up corresponding vibrations in the. membranes 42 and 43.

It will be understood that the adjustment feature could also be accomplished by having portions of the frames relatively movable in respect to each other in a suitable manner readily apparent to one sln'lled' in the art.

Instead of connecting the two membranes with adjustable tensioning means as heretofore described, these membranes, as shown in Fig. 9 maybe connected together by wire or by an equivalent tension member 48. The vibrations from the telephonic unit 49 may be transmitted to the wire 48 through a connection 50 which in this modification is positioned at right angles to the wire 48.

If desired the membranes may be tufted together at a plurality of ponts, for instance as shown in Fig. 10. In this figure the two membranes '51 and 52 are tufted together by suitable means at 53. The vibrations produced by the telephonic unit 54 are preferably conducted to the membranes at one of the points where the membranes are tufted together. It is to be understood that membranes 51 and 52, however, may be tufted together without actually being in contact in a manner, for instance, as illustrated in Figs. 8 or 9.

If desired three or more membranes of the same or diiferent sizes or shapes may be drawn together at a common point so that each membrane will be maintained under tension by the other membranes connected thereto. Fig. 11 shows an assembly of this tvpe, wherein membranes 55, 56 and 57 are drawn and held together at a central point 58, and thus maintain each other under tension. The vibrations set up in the telephonic unit 59 may be applied to these three membranes simultaneously by means ofa reed 60 which is connected to the membranes at the point 58. A suitable frame 61 isfprovided to support the membranes at their periphcries.

Instead if drawing two membranes together so that each will hold the other under tension, the membranes may maintain each other under tension by being held apart, such for instance as by a rigid post. For example, in Fig. 12 the'membranes 62 and 63 are clamped by means of nuts 64 and 65 respectively to a bolt or rod 66 which spaces the membranes so far apart from each other that they are under the desired tension.

These memberanes are secured at their peripheries to :a suitable frame 67..

From the above it will be apparent that in accordance with this invention the loud speaker may comprise one, two or more membranes, each capable of emitting and reproducing sounds in accordance with vibrations applied thereto, as by a. telephonic unit of standard construction. The periphery of any membrane may be circular, square or otherwise as desired. When the speaker ineludes more than one membrane, the mem-- branes may be of the same size or may be of different sizes. It may be that a membrane of small size, is best to reproduce notes and sounds of ahigh register and that membranes of. large area are best adapted to reproduce sounds and notes of a low regis ter. TlllS invention permits the associatlon shapes and different tensions whereby the speaker is perfectly adapted to notes and sounds of high and low register and inter-- mediate register. At the same time, as before stated, each membrane may be maintained under tension by another membrane or membranes associated therewith, or by independent tensioning means, and all the membranes vibrate to translate into sound the vibrations applied thereto by the telephonic unit, each membrane serving in accordance with its size and other character istics.

As aforesaid, any suitable means may be provided for placing any membrane under tension along lines which converge inward of its periphery. so long as such means do not interfere with the proper vibration of the membrane. Accordingly the membrane may be tensioned and anchored inward of its periphery to any resilient means which permits vibration of the membrane.

Another form for carrying out the purpose of tensioning the membranes may be stated as follows: The periphery of a membrane is fastened to a suitable frame and the center of the membrane extended until the material of the membrane becomes tensioned. While the membrane 1s under this tension a coating of only slightly compressible substance is applied. The tension on the membrane may be thereafter released but the membrane will not completely go back to its original position due to the presence of the coating substance which opposes and balances to an extent the contractional effort of the membrane. The membrane material, therefore, remains tensioned to some extent after the external tension has been released, but it does not have the stiffness desired for" the reproduction as described herein. It may also be understood instead of applying a coating substance as noted that any suitable material or sustaining frame may be associated with the membrane after ithas been tensioned thereby maintaining the membrane under tension after the release of the original tension so that it will vibrate in response to means acting on the membrane for vibrating the same.

It is usually immaterial on which side of any membrane the telephonic unit is placed, and if there are two mutually tensioned membranes, the telephonic unit may be placed on either side of them or between them in a desired position.

The membranes when vibrating cooperate and may be considered as a unit vibrating element or diaphragm. I I

Any suitable material may be used for any of the membranes, and it is to be understood that there is no restriction to any particular substance. Suitable substances for this purpose may be linen; muslin, cloth, skin,

leather, and natural or artificial membranes, such as cellulose-xanthate. It is to be understood that one membrane may be made of one material, and another membrane made of another material.

When referring to cloth membrane, for instance, it is to be understood that the membrane material may be of ordinary fabric which is preferably closely woven. Also, when the cloth, or fabric of that nature, is employed ready for use the pores thereof are substantially filled by the coating herein mentioned.

It is not essential to follow any precise order of placing the membranes in position and causing them to be tensioned. For instance, it is immaterial whether the shrinking compound, if used, be applied to the membrane before or after the membrane is attached in place. If there are two'mem brane-s they may be first attached to the frames, then drawn together, and then treated with a shrinking substance; or they may .be first attached together, then secured to the frame, and then treated with the shrinking substance; or first one membrane may be secured to the frame, with or without having the shrinking substance applied thereto, then the other membrane may be attached to the first one, and then to the frame, and then the shrinking substance applied to the second membrane.

As many changes can be made in the above construction" and as many different. embodiments of thls invention can be made general plane of the periphery, said memb'rane as so tensioned having substantially all parts therdof within a surface generated by a straight line having one end at said point and passing through and following the contour of the periphery of the membrane, and means for applying sound reproducing vibrations to said membrane.

2. A sound reproducer of the character described, comprising, in combination, a supporting frame, a vibratory membrane fastened to said frame, resilient means maintaining said membrane under tension along lines converging inward of its periphery and toward a point located outside of the general plane of the periphery, said membrane as so tensioned having substantially all parts thereof within a surface generated by a straight line having one end at said point and passing throu h and following the contour of the periphery'of the membrane, and means for applying sound reproducing vibrations to said membrane, said resilient means including a vibratory member to which said membrane is connected. v

3. A sound reproducer ofthe character described, comprising, in combination, a supporting frame, a vibratory membrane fastened to said frame, resilient means maintaining said membrane under tension along lines converging inward of its periphery and toward a point located outside of the general plane of the periphery, said membrane as so tensioned having'substantially all parts thereof within a surface generated by a straight line having one end at said point and passing through and fol lowingthe contour of the periphery of the membrane, and means for applying sound reproducing vibrations to said membrane, said resilient means including a second vibratory membrane joined to the first membrane.

4. A sound reproducer of the character described, comprising, .in combination, a

supporting frame, a vibratory membrane tially all parts thereof within a surfacegenerated by' a straight line having one end at said point and passing through and following the contour of theperiphery of the membrane, and means for applying sound reproducing vibrations to said membrane,

said resilient means including a second vibratory membrane, said membranes being connected to each other substantially at their centers.

5. A-sound reproducer of the character described, comprising, in combination, a supporting frame, a vibratory membrane fastened to said frame, resilient means maintaining said membrane under tension along lines converging inward of its periphery and toward a point located outside of the general plane of the periphery, said membrane as so tensioned having. substantially all parts-thereof within a surface generated by alstraight line having one end atisa d point and passing through and following the contour of the periphery of the membrane, and means for applying sound re producing vibrations to said membrane, said resilient means including a second vibratory membrane, said membranes being tensioned toward each other.

6. A sound reproducer of the characterdescribed, comprising, in combination, a supporting frame, a vibratory membrane fastened to said frame,' resilient means maintaining said membrane under tension along lines converging inward of its periphery and toward a point located outside of the general plane of the periphery, said membrane as so tensioned having substantially all parts thereof within a surface generated by a straightline having one end at said point and passing through and following the contour ofthe periphery of the membrane, and means for applying sound reproducing vibrations to said membrane, said resilient means including a second vibratory membrane joined to said first membrane,

. said membranes being of different sizes.

7. A sound reproducer of the character described, comprising, in combination, a'

supporting frame, a vibratory membrane fastened to said frame, resilient means maintaming sald membrane under tension along lines converging inward of its periphery and toward a. point'located outside of the;

general plane of the periphery, said membrane as so tensioned having substantially all parts thereof within a surface enerated at said.

point and passing through and following the contour of the'periphery of the membrane, and means for applying sound reproducing vibrations to said membrane, said resilient means including a second vibratory membrane, joined to said first membrane,

said membranes being of different sizes and being connected together at their center's.

8. A: sound 'reproducer of the character described, comprising, in combination, a supporting frame, a vibratory membrane mounted in association with said frame, resilient means maintaining said membrane under tension along lines converging inward of its periphery and toward a point located outside of the general plane of the periphery, said membrane as so tensioned having substantially all parts thereof within a surface generated by astraight line having one end at said point and passing through and following the contour of the periphery of the membrane, and means for applying sound reproducing'yibrations to said membrane, said resilient means being adjustable whereby thetension on the membrane may be varied. f

9. A sound 'reproducer of the character described, comprisin in combination, a supporting frame, a vibratory membrane fastened to said frame, resilient means maintaining said membrane under tension along lines converging inward of its periphery and toward a point located outside of the general' plane of the periphery, said'membrane as so tensioned having substantially all parts thereof within a surface generated by a straight line having one end at said point and passing'through and following the contour of the periphery of ,the membrane, and means for applying'sound reproducing vibrations to said membrane, said resllient means including a second vibratory membrane, said membranes beingconnected together by an adjustable device whereby the tension force of the membranes on each other may be varied.

10. A sound reproducer of the character described, comprising, in combination, two oppositely disposed substantially vertical supporting frames connected together, two coated cloth membranes fastened one to each of said frames and drawn together to create tension in each and connected together asso tensioned, and means for applying sound reproducing vibrations to said membranes.

11.--A sound reproducer of the character described, comprising, in combination, two oppositely disposed substantially vertical supporting frames connected together, two

coated cloth membranes fastened at their producing vibrations to said membranes.

12. A sound reproducer of the" character described, comprising, in combination, two oppositely disposed substantially Vertical supporting frames connected together, two

coated cloth membranes fastened at their edges, one to each of said frames, and drawn together to create tension in each and as so tensioned' connected together at their central points, means for applying sound reproducing vibrations to said membranes, and means for adjusting the tension in said membranes after they have been joined.

13. In a loud speaker, in combination, an open rectangular supporting frame, a cloth membrane fastened to said frame on one side thereof, a second frame supported by said first frame in proximity ,to the other side of saidfirst frame, a second cloth membrane of relatively smaller size than the first membrane mounted on said second frame, said membranes being joined together at their centers by materially drawing said larger membranev out of a plane passing through its periphery thereby placing both of said membranes under tension, said membranes having'their stifl'ness increased by application of a shrinking material, said membranes being thereby balanced against each other and each being under tension, and means for applying sound reproducing vibrations tosaid membranes while under said balanced tension.

- opposing one point in one membrane against a point in the other membrane thereby distorting each point out of the periphery of its membrane so that each membrane will take a position which falls within a surface generated by a straight line having one end at its said point and passing through and following the contour of its periphery, and

means for applying sound reproducing vibratlons to sa d membranes.

WILLIAM B. WHITMORE. 

